Due to increasing scarcity of fluid fossil fuels such as oil and natural gas, much attention is being directed towards converting solid carbonaceous materials such as coal, oil shale, tar sands, uintaite and solid waste to liquid and gaseous hydrocarbons by pyrolysis. Pyrolysis can occur under nonoxidizing conditions in a pyrolysis reactor in the presence of a particulate source of heat to yield as products pyrolytic vapors containing hydrocarbons and a particulate carbon containing solid residue. The particulate source of heat for effecting the pyrolysis of the carbonaceous material can be obtained by oxidizing carbon in the particulate carbon containing solid residue in a combustion chamber.
There are many problems associated with this scheme of using a pyrolysis reactor and a combustion chamber for obtaining hydrocarbons from solid carbonaceous materials. One of these problems is the caking of coal along the walls of the pyrolysis reactor. Experience with agglomerative coals, particularly Eastern United States coals, indicates that these coals have a tendency to agglomerate in a reactor, especially along the walls of the reactor.
Another problem is how to transfer the particulate carbon containing solid product from the pyrolysis reactor to the combustion chamber while at the same time keeping oxygen in the combustion chamber out of the pyrolysis reactor. If oxygen manages to leak into the pyrolysis reactor, the value of the hydrocarbon product is reduced and a violent explosion may occur.
A third problem is how to maximize production of carbon dioxide and minimize production of carbon monoxide in the combustion zone to maximize recovery of the heating value of the carbon containing solid residue during oxidation. The kinetics and thermodynamic equilibrium of the oxidation of carbon favor increased production of carbon monoxide relative to carbon dioxide at temperatures greater than about 1200.degree. F. at long residence times when there is a stoichiometric deficiency of oxygen. Since pyrolysis of carbonaceous materials often is conducted at temperatures greater than 1200.degree. F. and can approach temperatures higher than 2000.degree. F., it is necessary to form a particulate source of heat having temperatures greater than 1200.degree. F. In addition the particulate carbon containing solid residue is only partially oxidized in a stoichiometric deficiency of oxygen to form the particulate source of heat. Thus production of carbon monoxide inevitably occurs during the oxidation step of the particulate carbon containing solid residue. The carbon monoxide formed represents a loss of thermal efficiency of the process.
Therefore, there is a need for a process and an apparatus for obtaining values from a solid carbonaceous material by pyrolysis which are useful for agglomerative coals; which, when a particulate carbon containing solid residue of pyrolysis of the carbonaceous material is oxidized to form a particulate source of heat to pyrolyze the carbonaceous material, prevent oxygen from entering into the pyrolysis reaction; and which maximize production of carbon dioxide while minimizing production of carbon monoxide.